/*
 * @Autor: lycheng
 * @Date: 2020-01-07 08:51:50
 */

(function() {
    self.onmessage = function(e) {
        transAudioData.transcode(e.data)
    }

    let transAudioData = {
        transcode(audioData) {
            let output = transAudioData.to16kHz(audioData)
            output = transAudioData.to16BitPCM(output)
            output = Array.from(new Uint8Array(output.buffer))
            self.postMessage(output)
                // return output
        },
        to16kHz(audioData) {
            var data = new Float32Array(audioData)
            var fitCount = Math.round(data.length * (16000 / 44100))
            var newData = new Float32Array(fitCount)
            var springFactor = (data.length - 1) / (fitCount - 1)
            newData[0] = data[0]
            for (let i = 1; i < fitCount - 1; i++) {
                var tmp = i * springFactor
                var before = Math.floor(tmp).toFixed()
                var after = Math.ceil(tmp).toFixed()
                var atPoint = tmp - before
                newData[i] = data[before] + (data[after] - data[before]) * atPoint
            }
            newData[fitCount - 1] = data[data.length - 1]
            return newData
        },
        to16BitPCM(input) {
            var dataLength = input.length * (16 / 8)
            var dataBuffer = new ArrayBuffer(dataLength)
            var dataView = new DataView(dataBuffer)
            var offset = 0
            for (var i = 0; i < input.length; i++, offset += 2) {
                var s = Math.max(-1, Math.min(1, input[i]))
                dataView.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7fff, true)
            }
            return dataView
        },
    }
})()